1. Field of the Invention
The present invention relates to a flow rate control valve for controlling a flow rate of a fluid flowing through a fluid passage. In particular, the present invention relates to a proportional type flow rate control valve using a driving source which is rotatably driven by an electric signal.
2. Description of the Related Art
A conventional flow rate control valve controls a flow rate of a pressure fluid by changing an area of a passage provided in a valve through which the pressure fluid flows, for example, when the pressure fluid is supplied to or discharged from an actuator.
The flow rate control valve comprises a pilot chamber including a diaphragm which is spread in a main valve body. A diaphragm is flexibly bent by a pilot pressure supplied to the pilot chamber for thereby integrally displacing the diaphragm and a valve plug. Thus, the fluid passage is opened/closed.
In the conventional flow rate control valve, the valve plug is opened/closed by the pilot pressure. However, it is difficult to control an opening degree of the valve plug highly accurately at a desired position based upon the pilot pressure, for the following reason.
Specifically, it is difficult to control the pressure of the air supplied as the pilot pressure highly accurately due to the fluctuation in pressure in a pressure fluid supply source. Further, the pilot pressure supplied to the pressure chamber may not correspond to the displacement amount of the valve plug.
It is therefore a general object of the present invention to provide a flow rate control valve which adjusts an opening degree of a valve plug reliably and highly accurately by controlling an axial displacement amount of a first movable member based upon an amount of rotation of a driving source driven by an electric signal, making it possible to highly accurately control a flow rate of a pressure fluid.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.